The invention relates to an apparatus and method for trimming signatures and, more particularly, to a system for obtaining high quality, precision trim cuts of signatures.
Post press signature finishing equipment including such items as folders, rotary trimmers, and various types of stackers, transporters and palletizers are regularly being required to handle greater rates of throughput as printing presses are continually being developed with increasingly fast operating speeds as otherwise high production speeds can be quickly lost post press. For rotary trimmers, this means that the knife needs to be able to maximize the number of cuts, e.g. 15-30 million trims, before requiring maintenance for sharpening or replacement of the cutting surfaces thereof. With high throughputs, trimmers undertake more cuts in a shorter period of time so that if the blade needed maintenance after a relatively few number of cuts there would be unduly frequent downtime for the production line due to the in-line rotary trimmer. This is especially undesirable if the knife starts creating low quality cuts in the middle of a press run requiring interruption of production for knife maintenance.
In rotary trimmers, proper setting of the clearance gap between the rotary knife and anvil is extremely important as that will in large part determine whether the trimmer generates high quality trims over a long knife life. Thus, maximizing knife life is of paramount concern because resharpening the knives is expensive, especially if it goes dull during a press run, as mentioned. Assuming the proper knife/anvil gap is set, they will cooperate with each other to cut or sever edge portions of the signatures with a scissors-like action generating clean, square cut surfaces. However, if this gap is too small or tight, the knife will quickly dull due to the excessive applied force at the cutting edges thereof. As opposed to a scissor-like severing action applied to the signatures, the dulling knife and anvil will exert more of a tearing or ripping action that generates fuzzy cut surfaces. On the other hand, if the gap is too large or loose, then the knife/anvil will not cut at all. Because the difference between a properly set knife and an improperly set knife can be the result of a change in the gap of only thousandths of an inch, setting of the knife/anvil gap needs to be a precise operation.
Currently, rotary knives of trimmers are usually adjusted by very low wage operators whose turnover rate generally is very high. A rough adjustment mechanism is provided to advance the knife toward a lower anvil that is mounted for some vertical overlap with the knife. The operator is supposed to select a feeler gauge with a thickness corresponding to the gap between the blade and anvil needed to generate high quality trim cuts for the particular sheet material to be trimmed. The operator carefully inserts the gauge into the cutting area between the knife and anvil and holds it there with one hand while reaching back with their other free hand to operate the adjustment mechanism for advancing the knife until the gauge is clamped between the knife and anvil. Then, using the adjustment mechanism the operator slightly backs up the knife just enough to allow them to free the gauge.
Of course, at this point the gap is necessarily larger than the gauge thickness so that already it is likely that there will be some quality concerns in cutting with the knife so set. Also, requiring the operator to insert the feeler gauge into the cutting area brings them dangerously close to cutting surfaces on the rotary knives increasing chances for injury. Moreover, as is apparent, this is an arduous procedure that frequently is just not done by low wage operators who instead try to eyeball the adjustment of the knife so that there is the correct gap between it and the anvil.
After this initial set-up, operators are instructed to let the rotary trimmer run for about fifteen minutes, and to then recheck the gap to determine whether the knife/anvil spacing has shifted due to thermal expansion of the knife assembly, and thus if the knife needs to be backed up to maintain the gap at its desired size. However, it has been found that it is very rare for operators to ever undertake this secondary check of the knife/anvil spacing especially since it is inefficient in that it requires the rotary trimming line to be shut down while the rechecking takes place. Since it is the usual case that the knife/anvil gap is not rechecked, it is much more likely that the knife life will be seriously compromised due to thermal expansion.
Directing ambient air into a shroud extending about the knife has been attempted to address the problem of excessive heat at the cutting edges which can cause the ink and varnish at the cut edges to smear and can also cause burning of the cut edges. However, this approach will not be satisfactory in avoiding the reduction in size of the knife/anvil gap during trim cutting operations as heat is also generated at other portions of the knife assembly beyond just at the knife head.
Manufacturers of rotary trimmers and the knives thereof want to be able to market their machines based on how many high quality trims one can expect to obtain before knife maintenance should occur. In this way, their customers can plan for knife maintenance to avoid generating excessive amounts of spoiled product, i.e. signatures with poorly cut surfaces by dull knives. In other words, customers want to be able to plan press runs so they will not be started with a knife that will need to be sharpened or replaced in the middle of the run, which also increases undesirable downtime, as previously discussed.
Certain known variables relating to the paper to be cut such as type, content, weight and thickness, for example, as well as operating speed of the trimmer can be factored in to allow manufactures to determine the knife life a customer can expect. However, the current situation where human operators are required to properly set-up the trimming machine as set forth earlier make such determinations virtually impossible as it has been found that significant inconsistencies in knife life and trim quality arise between different customers that cannot be attributed to differences in the other known variables. Of course, this makes sales of rotary trimmer knifes more difficult as very meaningful statements regarding knife life correlated to the known variables are hard to substantiate. Instead, very large ranges for knife life are specified, e.g. 15-30 million trim cuts, and even so, reaching this range still depends on proper set-up of the machine including the knife/anvil gap spacing.
Accordingly, a need for a rotary trimmer apparatus and signature trimming method exists that provides precision adjustments of the knife/anvil gap to be made in an accurate, easy and efficient manner. Further, a rotary trimmer apparatus and method that allow for high quality trims to be consistently made over long knife lives would be desirable.
In accordance with the present invention, a rotary trimmer apparatus and signature trimming method are provided that allow the gap spacing between a rotary knife and anvil to be easily and precisely set prior to operation of the apparatus with the knife staying sharp for a maximum number of trims to generate high quality cuts therewith, without the need to recheck the set knife/anvil spacing as previously required. To this end, the present invention allows an operator to incrementally shift the rotary knife to one of the plurality of predetermined spaced positions relative to the anvil without the need for separate special tools or the like. Further, during operation, the knife is maintained at the selected position via a temperature control system for a rotary spindle shaft to which the knife is mounted. The temperature control system maintains the temperature of the rotating shaft substantially constant between its temperature during set-up to its temperature during trim cutting operations. In this manner, axial shifting of the knife due to temperature changes of the shaft, especially thermal expansion of the spindle shaft during cutting operations is substantially obviated, thus keeping the knife at its selected spaced position relative to the anvil ensuring that the knife does not prematurely dull and/or generate less than high quality precision cuts. Accordingly, by way of the present invention, manufacturers of these trimmers and rotary knives will be able to more precisely determine their useful life as a function of various known operating conditions, e.g. paper type, number of folds in the signature books, and operating speeds, as the knife is readily accurately shifted to the desired spaced position relative to the anvil and is maintained thereat, even during high throughput cutting operations of the rotary trimmer, e.g. up to 110,000 signatures per hour.
It has been found that unwanted linear shifting of the knife due to thermal expansion during trimmer operations occurs primarily because of the expansion that occurs at the knife spindle shaft which shifts the knife closer toward the anvil along the shaft axis increasing the forces at the cutting edges of the knife which, in turn, prematurely dulls these edges shortening knife life. Accordingly, the temperature control system herein keeps the temperature of the shaft substantially constant from when the knife/anvil gap spacing is set to its temperature during trim cutting operations. Although the preferred mode of operation is by directing a cooling medium, e.g. cool air, into heat transfer relation with the spindle shaft, it is also contemplated the shaft could be subjected to high heat so that when the knife position is set, the shaft is at a pre-heated high temperature and subsequent heat generation in the shaft bearings will not cause a temperature rise in the shaft. Alternatively, such as where spindle shafts are open as discussed further herein, high volumes of ambient air can be discharged at the shaft so that the shaft does not experience a significant temperature rise during trim cutting operations. The temperature control system herein in whichever form that is employed is effective to keep the shaft at a substantially constant temperature during set-up and trim cutting operations.
Herein, substantially constant temperature of the spindle shaft means the system keeps any temperature differential that develops to a minimum so that any knife shifting due to this differential will be so minor as to not affect the quality of the cuts obtained or be a detriment to the life of the knife. The differential that is acceptable depends on several factors, such as the length of the shaft from where it is held in its forwardmost bearing to the end of the knife and the shaft material, as well as the characteristics of the signature being trim cut.
By way of example and not limitation, to keep shaft expansion to an amount that is not detrimental to trim quality and knife life such as 0.0005 inch and with the spindle shaft being of alloy steel material and having a length of 2.0 inches from bearing to knife end, the temperature differential is preferably kept to approximately 15xc2x0 F. by the temperature control system herein. The maximum amount of knife shifting that is tolerable is approximately 0.001 inch. In this instance, the temperature differential can be approximately 30xc2x0 F. To obtain the allowable temperature differential for a particular amount of linear expansion that is tolerable, this amount of linear expansion of the shaft is divided by the product of the operable shaft length, in this instance 2.0 inch, and the coefficient of linear expansion per linear inch, e.g. 0.0000160 in/xc2x0F. for an alloy steel knife spindle shaft.
With the preferred cooling of the shaft provided by the present temperature control system, thermal expansion of the knife spindle assembly is minimized thus maximizing the number of trims obtained with the knife that are of a consistently high quality, and avoiding the need to recheck the knife/anvil spacing after running of the trimmer apparatus as was previously required. More particularly, the present preferred cooling system can include a temperature controlled housing or knife spindle block. The spindle block includes a chamber through which the knife spindle shaft extends. Preferably, air is used as the cooling medium and is fed into the knife spindle block, circulates within the internal chamber thereof, and then exits the block to keep the internal space of the housing at a constant, relatively cool operating temperature, e.g. 80xc2x0 F., at which significant axial shaft expansion will not occur. In this regard, it is preferred that the air be cooled before being fed to the spindle block to below room temperature to improve the cooling capacity of the system.
After exiting the knife spindle block, the cool air can be directed at the periphery of the knife via an adjustable hose with an outlet nozzle that is pointed at the knife edge of the trimming knife such that the cool air impinges thereon. Thus, the present cooling system can cool both the knife spindle and trimming knife simultaneously using a common cool air source. In addition, focusing the cool air directly at the knife cutting edge is much more effective in keeping the heat generation thereat to a minimum versus simply supplying a knife shroud with ambient air flow therethrough. Where the knife is of a solid body design with an integral serrated cutting edge at its periphery versus having a plurality of removable segments, the temperature rise at the cutting edge is more significant, e.g. 170xc2x0 versus 120xc2x0, thus rendering the auxiliary cooling of the knife edge more important in achieving a large number high quality trim cuts therewith. Even with the segmented knife, the auxiliary cooling herein is beneficial in reducing heat build-up at the cutting edges and the low quality product and product spoilage this can create.
As previously mentioned, the present rotary trimmer apparatus allows an operator to very easily and accurately position the knife relative to the anvil. For this purpose, the rotary trimmer apparatus preferably has a control knob that is calibrated for different predetermined spaced positions of the knife relative to the fixed anvil so that turning of the knob indexes the knife between the different positions. This allows an operator to determine which spacing of the knife and anvil generates the best cuts for particular operating conditions and so that when these operating conditions are repeated, they will easily be able to obtain the same knife/anvil spacing and reproduce the high quality cuts they need.
The control knob is remote from the cutting area between the knife and anvil and does not require the use of a feeler gauge or the like so that the operator can remain at the remote position of the control knob during precision setting of the knife position relative to the anvil. Accordingly, no longer is there a need for an operator to get near the cutting area and endanger themselves with the sharp cutting edges of the rotary knife as could previously occur when using the feeler gauge.
For precision shifting of the knife, turning of the control knob rotates a threaded actuator shaft that is operable to translate the spindle block carrying the spindle and knife therewith. An internally threaded member fixed to the spindle block cooperates with the threads on the actuator shaft so that turning of the control knob causes the spindle block to translate on a slide fixture therefor. However, with normal thread tolerances, there will be a backlash after shifting of the spindle block that is unacceptable for the precision movements of the knife needed herein, i.e. on the order of thousandths of an inch. While obtaining precision ground threads is possible, manufacture of these types of threads would undesirably increase the cost of the present trimmer apparatus.
Accordingly, the internally threaded member attached to the spindle block is preferably in the form of a take-up member that is split into opposing portions that are adjustable relative to each other. Thus, the take-up member can be provided with internal threads of a normal tolerance while allowing the portions thereof to be adjusted to take up the slack between the threads of the take-up member portions and the actuator shaft threads while still allowing an operator to rotate the shaft for shifting of the spindle block without seizing. In this manner, the present adjustment mechanism provides precision movements of the spindle block without necessitating the increased cost associated with high precision ground threads. A further advantage of the take-up member is that it can be of a softer material than the actuator shaft, e.g. brass versus steel. Even as the brass take-up member wears, the take-up member portions can be adjusted to accommodate for the extra play in the threads the wear creates thus maintaining the precision movements provided by the present adjustment mechanism over time.
In another aspect of the present invention, a method of maximizing the knife life in a rotary trimmer apparatus is provided. The method includes providing an adjustable rotary knife having at least one peripheral cutting surface and a rotary anvil to form a signature cutting area, adjusting the knife to one of a plurality of predetermined known spacings from the anvil by a user at a position remote from the cutting area, running the signatures through the cutting area and cutting edge portions off therefrom, and keeping thermal expansion of a rotary spindle shaft carrying the rotary knife to a minimum to maintain the knife at the predetermined spacing from the anvil during cutting operations so that the peripheral cutting surface of the knife stays sharp over a maximum number of cuts therewith to generate square cut surfaces of the signatures.